Envelope for an electric device



April c. T. ULREY ENVELOPE FOR AN ELECTRIC DEVICE Original Fild Nov. 1, 1955 INVENTOR C: I (/ZFfY BY )71 ATTORN I Patented Apr. 6, 1937 UNITED STTES PATENT orsis ENVELOPE FOR AN ELECTRIC DEVICE Application November 1, 1933, Serial No. 696,180

- Renewed February 18, 1937 12 Claims.

The invention relates to electric devices, especially to an improved envelope therefor, and also to a new method for producing the same. In its more specific aspect the invention is directed to a novel envelope for a radiation producing electric device, and to the method for producing the same.

Although my invention is not limited to the X-ray field it will be described with reference to an X-ray tube because it finds immediate and especial application as an element thereof. X-ray tubes generally comprise an anode and a cathode located within a vitreous highly evacuated envelope. The envelope may be in the form of a cylinder having a small portion thereof which is thinner than the remaining portion of said envelope. This thin section is customarily of rectangular or curved contour, with the length of the section being equal to about one-fourth the circumference of the tube. The methods heretofore employed for rendering said section thinner than the remainder of the envelope involve the employment of an etching solution or a mechanical abrasive means. Both of these methods have inherent difficulties.

In both cases the forming of the window is a relatively slow and time-consuming task. The first method has the additional disadvantage in that an appreciable percentage of the envelopes is broken during this procedure of grinding to form a window. In order to obviate the above enumerated, as well as other disadvantages inherent in, and incidental to, the methods above outlined and, so that a novel type of window may be provided, I have developed the present invention.

Briefly, the invention comprises an envelope having a portion thereof in the form of a band extending entirely around the circumference thereof and measuring in thickness at great deal less than the remainder of the envelope and being of the same composition as the remainder of said envelope. The novel envelope is produced by heating a restricted band of said envelope and applying tension thereto to thin out the same at that restricted area.

An object of my invention is to provide an envelope having a thin window which envelope may be readily and inexpensively produced.

Another object of my invention is to provide an electric discharge device having an envelope with a thin window which thin window may be produced by an unskilled operator.

Still another object of my invention is to provide a new method for producing an envelope with a thin window.

Other objects and advantages of my invention will be readily apparent from the following description and drawing wherein,

Figure 1 illustrates an X-ray tube embodying my invention;

Figure 2 represents an enlarged cross sectional view taken on line IIII of Figure 1;

Figure 3 illustrates the means employed at onestep of my novel process;

Figure 4 is a cross sectional View taken on line IV-IV of Fig. 3;

Figure 5 illustrates the means employed at a later step of my invention and also illustrates the condition of the envelope at this stage;

Figure 6 is a cross sectional view taken on line VIVI of Figure 5.

As shown in Figure 1, the X-ray tube embodying my invention comprises an envelope 9 having an anode l 0, and a cathode l2 therein. The envelope 9 is air-tight and is composed of a vitreous dielectric material, such as glass. The envelope 9 has a body portion II which is in the form of an elongated cylinder. Extending into said cylinder l I and sealed thereto by fusion is a glass reentrant stem l 3 having a pinchor press M at the free end thereof. Sealed in said press M are a plurality of conductors l5, l6 and I! connected to the cathode I2. The conductors l5 and i6 extend exteriorly, as well as interiorly, of the envelope Q. A reentrant tube I8 is sealed by fusion to the other end of the cylinder H and-extends a short distance therein. A copper thimble l9 having its rim sealed to the free end of the tube it forms an air-tight hermetic seal therewith. The anode It and an anode extension 2!! carrying a heat radiator 21 are connected, as shown, to the thimble it]. Another reentrant tube 22 is ring-sealed to the inner wall of the cylinder i l and surrounds the anode Iii. A spring member 23 is secured to the anode and frictionally engages the interior surface of the tube 22 to aid in supporting the anode I0.

According to my invention the body portion of the envelope 9, which is in the form of a cylinder, has a section 38 thereof whose thickness is materially less than that of the remainder of the envelope so that the absorption of this section to radiations below the visible portion of the spectrum is materially less than that of the remainder of the envelope. As shown, the thickness of the band 30 is about one-third the general thickness of the remainder of the envelope. Of course, it is within the purview of my invention to have the band 30 of any desired thickness depending upon what I desire.

Although it is not absolutely essential tomy invention, I prefer that the outer diameter of the section shall be substantially the same as the outer diameter of the major portion of the cylinder l I. The thin band 39 is located opposite the free or target end of the anode it and the width of said band which may be of any desired magnitude is so chosen that most of the useful X-rays generated at the target may pass therethrough.

The X-ray tube heretofore described is assembled in the manner well known in the art. However, the novel step in the manufacture of the X-ray tube, and which is essentially a portion of my invention, is directed to the formation of a band window in the body portion of the envelope.

According to my invention the vitreous cylinder I I that is to form the body portion of the envelope is placed between a pair of chucks (diagrammatically shown in Figure 5) of a glass lathe. The jaws of said chucks tightly grip the ends of said cylinder II and are adapted to rotate in synchronism with each other and thus properly rotate the cylinder II. A pair of bands 3| and 32 composed of a highly refractory dielectric (asbestos) or other material are inserted over the cylinder I I in proper position and are spaced the desired distance apart. A plurality of nozzles 33 are spaced from and located around the periphery of the cylinder between the bands 3! and 32. A suitable gas or admixture of gases pass through said nozzles. These gases are ignited to produce flames which play directly upon that portion of the cylinder l l between the bands SI and 32 which serve as a bafiie to limit the heating of the glass to a particular area. The cylinder ll, together with the bafiles, is continuously rotated during the period that the gas flames strike the glass to heat and soften the same. After the glass between the baffles has been heated to the desired extent and has become sufficiently softened, the

v chucks are moved away from each other thus drawing the softened glass band between the baffies 3| and 32.

Throughout the drawing stage the cylinder II is continually rotated and the intensity of the flames may be reduced, but they are played upon said band 30 during this action. I have found that when the glass has become softened due to its elevation in temperature at the band portion thereof, and after drawing, that the glass at the band portion 38 recedes inwardly towards the central longitudinal axis of the cylinder. To rectify this phenomenon I have provided one end of the cylinder with a tightly fitting rubber stopper 34 and the other end of the cylinder with a rubber stopper 35 through which extends a tubular element 36 adapted to convey an inert gas, such as nitrogen, into said cylinder. During the period that the band is being drawn and immediately thereafter a gas, such as nitrogen, is forced under pressure into said cylinder through the element 36. The glass still being in a rather soft condition at the drawn band portion thereof is blown outwardly due to the gas pressure which I have created within the cylinder ll. Of course the gas pressure is so regulated that the softened band is not blown out to a large bubble.

A tool 31 having a flat plate 38 at one end thereof may be placed upon the cylinder and over the softened band of the glass so that as the pressure within the cylinder is built up it will merely force the softened glass out only as far as the outer surface of the cylinder 1 I. Thus the band 30 may be made thinner than the remaining portion of the envelope and may have the same outside diameter as the remainder of the envelope. Thereafter, of course, the cylinder H is dismounted from the chucks and the customary tube assembly takes place.

As a specific example, I have taken a glass cyl inder whose wall thickness measured about one hundred mils and heated a section 30 measuring about one-half inch in width. When the section 3! was sufficiently softened, the ends of the cylinder were pulled away from each other until the width of the section 39 measured about an inch and a half. During the drawing operations a gas pressure was created within the cylinder to force the section 38 in proper position so that its external diameter was the same as that of the remainder of the envelope.

Although my invention has been described with some particularity it is not to be limited thereby but is to be limited only by the prior art.

What is claimed is: 1. In combination with a plurality of electrodes,

of a vitreous envelope, a portion of said envelope with a vitreous envelope, said envelope having a portion thereof in the form of a band which is relatively thin as compared to the remainder of said envelope and which has a materially lower absorption to radiations below the visible portion of the spectrum than does the remainder of the envelope, said band extending'around the entire circumference of said envelope.

3. The combination of a plurality of electrodes with a vitreous envelope, a portion of said envelope intermediate the ends thereof being relatively thin as compared to the remainder of said envelope and having a materially lowered absorption factor to radiations below the visible portion of the spectrum than does the remainder of the envelope, said portion extending around the entire circumference of said envelope.

4. The combination of a plurality of electrodes with a vitreous cylindrical envelope of substantially the same diameter throughout most of its length, a portion of said envelope being in the form of a relatively thin band and having a materially lower absorption to radiations below the visible portion of the spectrum than does the remainder of the envelope, said portion extending around the entire circumference of said envelope.

5. The combination of a plurality of electrodes with a vitreous envelope, a section of said envelope being relatively thin as compared to the remainder of said envelope, one of said electrodes having an active portion, said section being located opposite said active portion of one of said electrodes and having a materially lower absorption to radiations below the visible portion of the spectrum than does the remainder of the envelope, said portion extending around the entire circumference of said envelope.

6. The combination of a plurality of electrodes with a vitreous envelope, a portion of said envelope being relatively thin as compared to th remainder of said envelope and having a materially lower absorption to radiations below the visible portion of the spectrum than does the remainder of the envelope, said portion extending around the entire circumference of the envelope, the outside diameter of said envelope being substantially constant throughout the greater part of its length.

7. In an X-ray tube the combination of a plurality of electrodes with a vitreous envelope, a portion of said envelope being relatively thin as compared to the remainder of said envelope, one of said electrodes having a target end, said portion having a materially lower absorption to X- radiation than does the remainder of the envelope, said portion extending around the entire circumference of said envelope and being located substantially opposite the target end of said electrode,

8. In an X-ray tube, the combination of an anode and a cathode with a vitreous tubular envelope, a portion of said envelope intermediate the ends of said envelope being in the form of an. annular, relatively thin band, said band having a materially lower absorption to X-radiation than does the remainder of the envelope, said anode having a target end, said band being located substantially opposite said target end.

9. In an X-ray tube, the combination of an anode and a cathode with Vitreous envelope, the body portion of said envelope being in the form of a cylinder, a portion of said cylinder being relatively thin as compared to the remainder of said cylinder, said portion having a materially lower absorption to X-radiation than does the remainder of the envelope, said portion extending around the entire circumference of the envelope, the outside diameter of said portion being substantially the same as that of the remainder of said cylinder.

10. Steps in the method of forming an envelope for an electric device comprising heating a complete circumferential section of a Vitreous hollow member, said section being located intermediate the ends of said member, applying pressure to the interior surface of said heated section toforce the same outwardly and drawing said heated section to reduce the thickness of the same.

11. Steps in the method of forming an envelope for an electric device comprising applying a heating flame to a section of a hollow vitreous member intermediate the ends of said member to elevate the temperature of said section for softening said section, rotating said member during the heating, drawing said section to' reduce the thickness of the same and applying'a fluid pressure tothe interior wall of said heated section to blow out the same.

12. A step in the method of forming an envelope for an electric device comprising directing a plurality of flames to a section of a hollow, cylindrical, vitreous member, said section being located between the ends of said member, baflling said flames to control the width of the section to be heated by said flames, rotating said member during the heating, drawing said section to reduce the thickness of the same, applying a gas pressure to the interior wall of said section to blow the same outwardly and controlling the diameter of the external wall of said. section when the same is being blown outwardly.

CLAYTON T. ULREY. 

